Patent GB-542730-A (GB)
Title: Improvements in or relating to arrangements for telegraph transmission
IPC: H04L25/22
Filed: 1940-06-21
Abstract: 542,730. Phantom systems. STANDARD TELEPHONES & CABLES, Ltd., (Braem, L. A. G. A., and Sobola, J.). June 21, 1940, No. 10702. [Class 40 (iv)] [Also in Group XL] In an impulse telegraph system, in which directcurrent code elements are translated into pairs of transient impulses for transmission over the line, the transient impulses are shaped by a network N, between which and the D.C. transmitting relay contact tr1 is located the transformer T which effects the translation. Thus incoming signals from line L do not have to pass through the transformer T. The invention may be used in conjunction with teleprinter exchange systems or with telephone circuits in phantom working. The circuit elements may be protected against excessive line voltages by insulating them from the earthed mounting plate and cover. While the D.C. transmitter feeds the relay TR over the lead SL, the D.C. receiver is fed over the lead RL by the contact rr1 of the impulse-receiving relay RR, whose windings w1, w2 form part of a hybrid transformer connected to a balancing network DB and a line L ; this relay translates transient impulses into D.C. impulses. The windings w1, w2 are shunted by a resistance R3 and condenser C3 respectively and both tend to hold the armature rrl on the contact it is engaging when current flows through them in opposite directions ; an effect somewhat similar to that of the Gulstad relay is produced by this " negative vibrating circuit," which is described with reference to Figs. 2a ... 2d (not shown) ; the movement of armature rr1 due to transient impulses received from line L is reinforced by the action of the circuit RR and battery B so that the D.C. impulses outgoing to lead RL have the correct wave-form. Phantom circuits. Three telegraph channels may be superimposed on a telephone quad as shown in Fig. 3, where the circuits between AA<SP>1</SP> and BB<SP>1</SP> are similar to that shown between AA<SP>1</SP> and BB<SP>1</SP> in Fig. 1. Two of the telegraph transmitters, tr1 and tr3, send to the two telephone pairs 1, 2 and 3, 4 over low-pass, filters LPF1, LPF2. The remaining telegraph transmitter tr2 sends phantomwise over leads PC connected to central tappings on the shunt capacities of the filters. Two ordinary telephone circuits TC1, TC2 together with a telephone phantom circuit PT are connected to the same quad 1, 2, 3, 4 as shown, and high-pass filters HPF1, HPF2 are provided, centre tappings on their shunt inductances being joined through an inductance L4. In an exchange system, Fig. 5, impulse-telegraph signals pass over a telegraph subscriber's line L, a telegraph exchange line EL, and a phantom circuit using the loops SL1, SL2 allocated to two of the telephone subscribers S1, S2, the connections of the phantom circuit being made as shown to centre tappings on resistancecapacity arms CR bridging the telephone pairs. Relays connected to the telephone subscriber's line at the exchange must have pairs of balanced windings so that dialling may not interfere with the impulse telegraphy. A single pair of subscribers loops SL1, SL2 may suffice (Fig. 4, not shown) or the phantom circuit may be extended from a district exchange DE to a main exchange ME over a second pair of telephone subscribers' loops TL1 TL2, the connection between the two pairs of loops being made through centre tappings on acceptor shunt arms, the inductances in which are so wound as to be series-opposing for the telegraph currents. Again, a teleprinter subscriber may be connected through D.C. sending and receiving lines to an impulse repeater which is of the kind shown in Fig. 1 and is located at a district exchange, and thence to a teleprinter exchange through a phantom circuit, Fig. 6 (not shown).